1. Field of the Invention
The present invention relates to a lead-free glass for covering electrodes and an electrode-formed glass substrate, which are suitable for producing a front substrate of a plasma display device (PDP), and a process for producing an electrode-formed glass substrate.
2. Discussion of Background
PDP is a representative large-screen full-color display device.
PDP is produced in such a manner that a front substrate to be used as a display surface and a rear substrate having a plurality of stripe- or waffle-shaped barrier ribs formed thereon are sealed as faced with each other, and discharge gas is introduced between such substrates.
The front substrate is one in which a plurality of display electrode pairs for inducing surface discharge are formed on a front glass substrate, and the electrode pairs are covered by transparent glass dielectrics. Electrode pairs usually consist of transparent electrodes made of e.g. ITO, and bus electrodes to be formed on a part of the surface of the transparent electrodes. As the bus electrodes, silver electrodes or Cr—Cu—Cr electrodes are used.
On the rear substrate, barrier ribs and a fluorescent layer are formed in addition to the electrodes.
The glass (dielectrics) covering electrodes on the front substrate, is formed by e.g. a method of transferring a green sheet containing a glass powder onto the electrodes, followed by firing, or applying a paste containing a glass powder on electrodes, followed by firing.
The glass forming a dielectric layer on the front substrate is required to be fired at a low temperature, to have high transparency after firing, and to have no coloration by silver diffused from the silver electrodes. Further, along with the production of a large-sized plasma TV, lately, the weight of a glass substrate has been brought up as an issue, and it has been studied to use a thinner glass substrate. However, in such a case, there is a concern such that the strength of the substrate may decrease. Therefore, in order to increase the strength of a PDP front substrate, it has been proposed to reduce the expansion coefficient of an electrode-covering layer (Non-patent Document 1).
Further, other than such a problem that the strength of the front substrate may decrease, there is a problem such as warpage or breaking of the front substrate during firing the glass powder, and the following method is suggested to solve such a problem. That is, with respect to the linear expansion coefficients αA and αB, of the glass substrate and the electrode-covering glass (electrode-covering layer), it is possible to prevent warpage or breaking of the front substrate by satisfying (αA−20×10−7/° C.)<αB<αA to bring the remaining stress of the glass substrate to be from −800 to +1,500 psi. Such an electrode-covering glass is particularly preferably one having a composition comprising, based on mass %, from 10 to 45% of B2O3, from 0.5 to 20% of SiO2, from 20 to 55% of ZnO, from 3 to 20% of K2O, from 0 to 10% of Na2O, from 0 to 5% of CuO+Bi2O3+Sb2O3+CeO2+MnO, and from 0 to 30% of Nb2O3+La2O3+WO3 (Patent Document 1).    Patent Document 1: JP-A-2006-221942 (such as “0013”, “0017”, or “0022”)    Non-Patent Document 1: 2007 SID INTERNATIONAL SYMPOSIUM DIGEST pp 389-392